1. Field of the Invention
This invention relates to the use of halogens as biocides to control biofouling in aqueous systems and in particular, those systems circulating water for cooling purposes such as water cooling towers, air conditioning systems and the like.
2. Description of the Prior Art
Biocides can be divided into two basic classifications: non-oxidizing biocides and oxidizing biocides. In general, the non-oxidizing biocides function primarily by altering permeability of the cell membrane of the microorganisms and/or interfering with some essential biological processes. Common non-oxidizing biocides include organo-sulfur compounds, quaternary ammonium salts, chlorinated phenolics, heavy metal compounds and others. Non-oxidizing biocides require longer contact times than oxidizing biocides in order to work but their activity usually persists longer. They therefore provide extended antimicrobial protection.
Oxidizing biocides generally react with proteins or other oxidizable groups on or within the organism resulting in cell injury or death. Oxidizing biocides are advantageous in water systems where there is low halogen demand and when a rapid kill or reduction in the number of organisms is required or preferred. As described in U.S. Pat. No. 4,297,224 to Macchiarolo et al, a variety of compounds are known to deliver oxidizing halogen to aqueous systems. Elemental bromine and bromine chloride have been used to deliver oxidizing bromine but their high volatility, toxicity and corrosive nature represent serious handling problems. Because of these difficulties, compounds which deliver oxidizing bromine for water treatment are often N-halogenated organics, bromates or an alkali metal bromide which is oxidized in situ by an oxidizing agent such as N-chlorinated compounds, gaseous chlorine, chlorine water or hypochlorite. N-halogenated compounds are usually solids but have low water solubility. Alkali metal bromides have good water solubility but require mixing with a strong oxidizing agent in order to generate the biocidal species, HOBr.
Oxidizing bromine has been delivered to aqueous systems by passing the water to be disinfected through a polyhalide anion-exchange resin where the cationic species are quaternary ammonium groups and the anions are polyhalides in the triiodide or tribromide form. As the water containing the microorganisms is passed through the resin bed, the corresponding hypohalous acid is formed. It is the biocidal action of the hypohalous acid released into the water which provides the desired microbial control. U.S. Pat. Nos. 3,462,363; 3,817,860; 3,923,665; 4,187,183; 4,190,529; 4,298,476; 4,420,590; and 4,594,301 describe biocidal uses of a quaternary ammonium polyhalide in resin form. They describe the use of polymeric quaternary ammonium polyhalides where the quaternary ammonium functionality is insoluble in water, and only the halogen becomes dissolved in the system being treated. Since the polymeric quaternary ammonium resin functions only as a solid support on which to hold the polyhalide anion, these systems suffer from the disadvantage that the water to be treated must be physically passed through a column. Also, the polyhalides must be regenerated in an additional step for repeat use of the solid support to be cost effective. It is further known that such resin beds can be partially or completely blocked during repeated use with small particles of resin, by mechanical attrition of the original resin particles, or with accumulating particulate matter filtered from the incoming water streams. Such blockages require removing the resin bed, sieving it to remove the fine particle size contaminant, and repacking the bed--all expensive and timeconsuming infringements on productive capacity. U.S. Pat. No. 4,581,058 also describes the the biocidal use of polymeric quaternary ammonium halides. Biocides have been delivered to aqueous systems in conjunction with polymeric dispersants as described in, for example, U.S. Pat. No. 4,451,376 to Sharp.
Certain quaternary ammonium monohalides are known to be effective non-oxidizing biocides, as described in German Patent DE No. 3,414,933 to Green et al. Quaternary ammonium monohalides have also been used as biocides in admixture with surfactants as described in German Patent No. 21 11 577 to Raziq et. al. Japanese Patent Publication No. 49/14,411 recognizes cetyltrimethylammonium bromide and cetylpyridinium bromide as having biocidal properties and also as starting material in the preparations of cetyltrimethylammonium tribromide and cetylpyridinium tribromide by reaction of the bromide with bromine in the presence of hydrobromic acid. The water insoluble tribromides produced are described as having biocidal properties.
In U.S. Pat. No. 3,152,073, Morton describes certain tetramethylammonium polyhalides as a water soluble compounds, solid in neat form, which can be added directly to water to achieve sterilization. Although this led Morton to recommend generally that a wide variety of tetraalkylammonium polyhalides which contain alkyl groups of six or fewer carbon atoms may be similarly used as solid, single reagents to achieve sterilization by direct addition to water, many of those recommended are not in fact sufficiently water soluble to produce useful active halogen concentrations (such as certain tetrabutylammonium polyhalides), are not in fact solids (such as certain dimethyl-propyl ammonium polyhalides) and thus are not available for use by the method disclosed. With the exception of Morton's use of the handfull of solid, water soluble tetramethylammonium polyhalides, nonpolymeric quaternary ammonium polyhalides have heretofore been unavailable in an economic, safe and efficient form as biocidal agents.
In the field of electrochemical battery systems certain unsymmetrical tetraalkylammonium salts are known to form liquids when complexed with bromine, as disclosed in United Kingdom Patent No. 2,005,064.
None of the known approaches to the control of biofouling provide a simple and economic means to deliver oxidizing halide at biocidally effective concentrations in an easily handled, liquid form. Nor do any of these approaches provide a simple and economic means to deliver oxidizing halide at biocidally effective concentrations together with non-oxidizing halide at biocidally effective concentrations and durations.
It is well recognized that aqueous systems exposed to the atmosphere provide bulk water environments in which microorganisms such as bacteria, algae, and fungi can live and reproduce. It is further known that within such environments colonies of such organisms can accumulate and grow in discrete masses or as surface deposits in which they are protected by their own metabolic products and debris, and that such accumulations may have a variety of adverse effects on the water systems and their uses. As used herein the term "biofouling" shall mean the overall effects of the existence, growth, and adverse consequences of such microorganism contaminations. As used herein the "control of biofouling" shall not mean disinfection, but rather shall mean the alleviation of said adverse consequences. It should also be noted that disinfection does not necessarily result in the control of biofouling.
It is a primary object of this invention to provide a method for controlling biofouling of aqueous systems by adding certain non-polymeric quaternary ammonium polyhalides to the aqueous systems.
It is a further object of this invention to provide quaternary ammonium polyhalide formulations which disperse, dissolve and facilitate the removal of floating and attached biofilm while simultaneously delivering active oxidizing halogen to the aqueous system.
It is a further object of this invention to provide quaternary ammonium polyhalide compounds and formulations that control biofouling by delivering both oxidizing halogen and non-oxidizing quaternary ammonium halide biocidal activity.